How Can I Separate Go Module Dependency Installation from the Build Process for Faster Docker Builds?

Separating Dependency Installation from Building in Go Modules

Go 1.11 introduced module support, which automates dependency installation during build and minimizes rebuilds. However, some developers prefer to manually fetch dependencies in a separate stage to leverage container caching and optimize rebuild speed.

vgo Solution

In earlier versions of Go, there was no native way to manually fetch dependencies. However, issue #26610 on the Go repository addressed this feature:

go mod download

This command allows you to manually fetch dependencies without running the build process. To use this command, you only need the go.mod and go.sum files in your project directory.

Docker Implementation

Here's an example of a Docker build script that implements a cached multistage build and utilizes go mod download:

FROM golang:1.17-alpine as builder
RUN apk --no-cache add ca-certificates git
WORKDIR /build

# Fetch dependencies
COPY go.mod go.sum ./
RUN go mod download

# Build
COPY . ./
RUN CGO_ENABLED=0 go build

# Create final image
FROM alpine
WORKDIR /
COPY --from=builder /build/myapp .
EXPOSE 8080
CMD ["/myapp"]

By implementing this separation of dependencies and build stages, you can take advantage of container caching for dependency installation and minimize subsequent build times.

Alternative Considerations

In addition to the go mod download approach, the article "Containerize Your Go Developer Environment – Part 2" explores another technique to optimize build speed: leveraging the Go compiler cache. Exploring both options can help you choose the best strategy for your specific project and environment.

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